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  1. #1
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    Default Low Brake Fluid Sensor Connection 86GT with 93 Cobra Master Cylinder 5 Lug Conversion

    Hey guys I have not found a thread, on any site, that talks about connecting the low brake fluid sensor wires from the 4 eyed cars to the popular 93 Cobra, 87-93, and SN95 Brake Master Cylinders.

    How can I make my low brake fluid senor in the dash work after doing the 5 lug conversion? I am using the 93 Cobra M/C. I can use the SN95 V6 unit but prefer the Cobra 1" bore.

    thanks.

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    My 86 dual reservoirs dont have a brake low fluid sensor. Did the gt's even have them?
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

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    Quote Originally Posted by Haystack View Post
    My 86 dual reservoirs dont have a brake low fluid sensor. Did the gt's even have them?
    Now that's a great point and question: what's the wire connector that connects to the Proportioning Valve; doesn't give the low fluid signal????

    Maybe 86 doesn't have it....hmm. I just assumed it would.... I would like to confirm this because I'm going with the 93 Cobra Brake Booster that does have the locator for one...

  4. #4

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    My 88 xr7 has one in the single reservoir. My 86 definately doesnt. I lost a brake line and it didnt give me a light or warning.
    2 1986 cougars (both 4 eyed and 5.0)
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    Quote Originally Posted by Haystack View Post
    My 88 xr7 has one in the single reservoir. My 86 definately doesnt. I lost a brake line and it didnt give me a light or warning.
    That's scary! So I wonder what the wires are for on top of the Proportioning Valve? I thought they were for this sensor. I never got a light on my brakes when I was driving my 86 so I never noticed if it had the sensor or not......

    If the 86 doesn't have it, then I'd love to know when it came into production and if I can modify a light into the dash now that I have it out for Heater Core and Evap install. I'd even be happy with just and IDIOT light using an LED.

    I'm hoping some others will chime in to further explain.

    Thanks @Haystack

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    FEP Senior Member BMW Rider's Avatar
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    The switch on the proportioning valve is for the brake warning light. In the event of a line failure, when the brakes are applied the spool in the proportion valve will move to the low pressure side and allow the switch to make contact and put the light on. In normal operation, the spool does not move, the switch pin sits in a detent in the spool so when it moves it pushes the pin in on the switch to make the contact. The switch, like most warning light senders, is the ground for the circuit.

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    Quote Originally Posted by BMW Rider View Post
    The switch on the proportioning valve is for the brake warning light. In the event of a line failure, when the brakes are applied the spool in the proportion valve will move to the low pressure side and allow the switch to make contact and put the light on. In normal operation, the spool does not move, the switch pin sits in a detent in the spool so when it moves it pushes the pin in on the switch to make the contact. The switch, like most warning light senders, is the ground for the circuit.
    So from what I understand you to be saying is: The switch on the PV IS the low fluid level switch. My reason for this question and as it stands: my be confused is because other in this thread state that the 86 doesn't have a low fluid level switch that illuminates on the dash. Perhaps I'm misunderstanding them or maybe we are talking about two different components.

    Primarily, I'm interested in sensing when my brake fluid level is low.

    I thought the 86 GT had such circuitry that operated off the switch on the Proportioning Valve wiring.

    I was hoping to somehow swap those wires over to have them work on the 93 Cobra Master Cylinder. During the 5 Lug Conversion, the stock Proportioning Valve gets gutted. IDK if this will effect the OEM switching process for the "warning Light?" In addition, I am thinking, now that you have enlightened me a bit on the PV circuit, that my idea of using the switching circuitry on the 93 Cobra Brake Reservoir would in the end be redundant, as the OEM PV for the 86 will handle this task....Is this correct? I notice you location is in Canada, I just want to make sure when you say "warning light" you don't mean brake lights.... No offense, sometimes different countries identity car parts differently. ie. bonnet = hood..lol Thanks for your reply for sure!

    I found a photo of PV cut-a-way. (THIS IS NOT an 86GT PV) Trying figure out how this would work as a low fluid warning circuit - mechanically....

    Name:  86 Mustang GT brake Proportioning Valve Cutaway.jpg
Views: 425
Size:  43.9 KB

    This is an 1986 Mustang GT Brake Pressure Control Valve:

    Name:  86 Mustang GT Brake Pressure Control Valve.jpg
Views: 417
Size:  89.7 KB
    Last edited by 1200; 02-28-2017 at 09:49 PM.

  8. #8
    FEP Power Member Ray Dog's Avatar
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    Could you wire the low level in parallel with the PV switch?
    It is already paralleled with the E brake on switch.
    You will then have the light come on for any of the 3 events.
    Ray
    86 Mustang LX 3.8 Convertible (bought new}
    65 Galaxie 500 XL 390 auto
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    Quote Originally Posted by 1200 View Post
    So from what I understand you to be saying is: The switch on the PV IS the low fluid level switch. My reason for this question and as it stands: my be confused is because other in this thread state that the 86 doesn't have a low fluid level switch that illuminates on the dash. Perhaps I'm misunderstanding them or maybe we are talking about two different components.

    Primarily, I'm interested in sensing when my brake fluid level is low.

    I found a photo of an 86 PV cut-a-way. Trying figure out how this would work as a low fluid warning circuit - mechanically....

    Name:  86 Mustang GT brake Proportioning Valve Cutaway.jpg
Views: 425
Size:  43.9 KB
    I think BMWRider is saying it is for warning of a line failure which would show up in the console warning center. When a line fails, the floating piece with the indent will shift over and close the circuit.

    I thought the warning light in the dash was only for the e-brake. I do know the SVO had the low oil sensor in the oil pan for engine oil level.
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  10. #10
    FEP Senior Member BMW Rider's Avatar
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    Quote Originally Posted by 82GTforME View Post
    I think BMWRider is saying it is for warning of a line failure which would show up in the console warning center. When a line fails, the floating piece with the indent will shift over and close the circuit.

    I thought the warning light in the dash was only for the e-brake. I do know the SVO had the low oil sensor in the oil pan for engine oil level.
    Quote Originally Posted by 1200 View Post
    So from what I understand you to be saying is: The switch on the PV IS the low fluid level switch. My reason for this question and as it stands: my be confused is because other in this thread state that the 86 doesn't have a low fluid level switch that illuminates on the dash. Perhaps I'm misunderstanding them or maybe we are talking about two different components.

    Primarily, I'm interested in sensing when my brake fluid level is low.

    I thought the 86 GT had such circuitry that operated off the switch on the Proportioning Valve wiring.

    I was hoping to somehow swap those wires over to have them work on the 93 Cobra Master Cylinder. During the 5 Lug Conversion, the stock Proportioning Valve gets gutted. IDK if this will effect the OEM switching process for the "warning Light?" In addition, I am thinking, now that you have enlightened me a bit on the PV circuit, that my idea of using the switching circuitry on the 93 Cobra Brake Reservoir would in the end be redundant, as the OEM PV for the 86 will handle this task....Is this correct? I notice you location is in Canada, I just want to make sure when you say "warning light" you don't mean brake lights.... No offense, sometimes different countries identity car parts differently. ie. bonnet = hood..lol Thanks for your reply for sure!

    I found a photo of PV cut-a-way. (THIS IS NOT an 86GT PV) Trying figure out how this would work as a low fluid warning circuit - mechanically....

    Name:  86 Mustang GT brake Proportioning Valve Cutaway.jpg
Views: 425
Size:  43.9 KB

    This is an 1986 Mustang GT Brake Pressure Control Valve:

    Name:  86 Mustang GT Brake Pressure Control Valve.jpg
Views: 417
Size:  89.7 KB
    The lamp in the instrument panel will light for either the E brake or a brake pressure failure. Since the circuit is completed by the ground side, either switch can illuminate the lamp. The console panel would be where the low fluid level light from the reservoir would appear assuming those years had that feature at all.

    I'm not certain on the conversion of the proportioning valve, but I believe it simply removes the pressure control valve for the front brakes and leaves the center shuttle spool in place to operate as normal. The job of the proportioning valve in a disc/drum combo is to allow pressure to build in the rear brakes first to allow the shoes to take up the slack before pressure builds in the fronts since disc brakes will start to apply almost immediately. Without it, you'd have hard front brakes with late to the game rears. The valve is actually a combination type with the shuttle valve in the middle for the warning light.

    Older four drum brake systems had a single circuit supplying all four wheels. Later, front and rear brakes were dual circuit to provide partial braking from front or rear in the event of a leak. The dual master cylinder will still apply some braking pressure to the good circuit. These had a simple shuttle valve to operate a light in a failure. Disc drum systems saw the addition of the proportioning valve to manage the differences in the brakes, later all disc systems don't necessarily need them if the brakes are balanced but in reality they often are not so a proportioning valve controls one end or the other to do that. Some trucks even had load sensing proportioning valves to vary the rear brakes based on the weight in the bed. And of course there are the manually adjustable proportioning valves for performance use to tune the front to rear balance.

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    Quote Originally Posted by Ray Dog View Post
    Could you wire the low level in parallel with the PV switch?
    It is already paralleled with the E brake on switch.
    You will then have the light come on for any of the 3 events.
    @Ray Dog, I spent the better part of last night reading as much as I could find on this subject, and I am arriving at the same potential challenge that you speak of in terms of parallel wiring the circuits. However, I think I will end up with some level of redundancy in terms of warning going this route. As I said, I'm still researching. In the end, the more warning I get on potential brake fluid level drop I can get, the better I'd feel. So, stay posted for my solution....

    Thanks a buch for you comment, for sure.

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    Quote Originally Posted by 82GTforME View Post
    I think BMWRider is saying it is for warning of a line failure which would show up in the console warning center. When a line fails, the floating piece with the indent will shift over and close the circuit.

    I thought the warning light in the dash was only for the e-brake. I do know the SVO had the low oil sensor in the oil pan for engine oil level.
    @82GTforME, I am in total agreement with your comments. I was certain less knowledgeable about these mechanicals when I started writing about them last night. I spent A LOT of time researching last night. I kinda have a better grip on the subject, however, I 'm still looking to master the concept for myself AND for others who may come along and read this thread...

    So thanks again for your comments as well. Hang around for my solution to possibly incorporating the 93 Cobra wiring into the 86 warning mix....maybe I can make something work better than the simple line-pressure level sensor. An earlier warning, say at the fluid bowl is what I think Ford progressed on to certainlly since 1993.

  13. #13
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    Quote Originally Posted by BMW Rider View Post
    The lamp in the instrument panel will light for either the E brake or a brake pressure failure. Since the circuit is completed by the ground side, either switch can illuminate the lamp. The console panel would be where the low fluid level light from the reservoir would appear assuming those years had that feature at all.

    I'm not certain on the conversion of the proportioning valve, but I believe it simply removes the pressure control valve for the front brakes and leaves the center shuttle spool in place to operate as normal. The job of the proportioning valve in a disc/drum combo is to allow pressure to build in the rear brakes first to allow the shoes to take up the slack before pressure builds in the fronts since disc brakes will start to apply almost immediately. Without it, you'd have hard front brakes with late to the game rears. The valve is actually a combination type with the shuttle valve in the middle for the warning light.

    Older four drum brake systems had a single circuit supplying all four wheels. Later, front and rear brakes were dual circuit to provide partial braking from front or rear in the event of a leak. The dual master cylinder will still apply some braking pressure to the good circuit. These had a simple shuttle valve to operate a light in a failure. Disc drum systems saw the addition of the proportioning valve to manage the differences in the brakes, later all disc systems don't necessarily need them if the brakes are balanced but in reality they often are not so a proportioning valve controls one end or the other to do that. Some trucks even had load sensing proportioning valves to vary the rear brakes based on the weight in the bed. And of course there are the manually adjustable proportioning valves for performance use to tune the front to rear balance.
    You are so correct @BMW Rider about the process that you have stated above. As I mentioned to other who have commented, I got an extensive amount of research in after reading your first reply. It spawned me on to research from a different perspective.: Understanding what the PV is all about in the first place. After finding that photo above, I started see the lights getting brighter in my mind.

    I'm now working on integrating the 93 Cobra low fluid level circuitry into the 86 setup. As yet, I'm not sure how it will play out, but I thinnnnk it's doable. We'll see.

    Hey, thanks so much for jumping in with your comments and information. It was most helpful.

    Dwayne

    BTW, once I get this all figure out, I plan on doing a quick write-up for others to find and learn from.....

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    I suggest a different route for the pump side of your brakes.

    A Lincoln Mark VII master cyl is a 1" bore rather than a 15/16" like is found in the 93 along with the SN95 or the 1 1/8 found in the SVO.

    Many people running the SVO master cyl without the large 73mm diameter single piston calipers report over assisted brakes with poor - very little - pedal travel before lockup. Too little brake rod movement.

    Many I've spoken to that use the 15/16 bore master cyl with stock foxbody booster talk about an under assisted feel with too much pedal travel before lockup and too much pedal pressure required for max braking and even perhaps normal driving situations. Too much brake rod movement for the fox booster.

    I am using the MarkVII master cyl with a simple line adapter available off the shelf at AutoZone. I gutted and plugged the front/rear bias portion of my stock proportioning valve and installed a Summit manual valve at the line Union on the passenger side. Master cylinder you want is part# m1858. Found at advance auto or AutoZone.

    My brakes work very well.

    A great friend of mine also has an 86 mustang and he runs SN95 rear brakes adapted to foxbody rear diff. I run an entire SN95 rearend. I run 99GT brake calipers with Baer rotors in front. He runs 2004 Cobra rotors and calipers up front. This setup functions flawlessly with both configurations and does not mess with the fluid lost warning indicator.

    Now I'm going to introduce somethibg new to worry about.

    I will say from experience that this light won't shield you from overloading brakes and ultimately boiling the brake fluid and losing braking. I did this once recently when one of my 99 calipers did what they are notorious for - stuck at part engagement - which build massive amounts of heat VERY quickly without noticeable input into the steering. I've since replaced the caliper and all is well again but my point is if you want the level of safety in your braking system that this thread seems to lay out as being desired then you need something to sense the temperature of your brake fluid. The warning light won't tell you when the DOT4 is blowing out from the sides of the seal on the master cyl due to heat expansion and is going to push past the seals in your master cyl due to extreme master cyl metal expansion at high heat. There is still enough fluid there that the light won't come on.

    I guess we could call it a down side of the more modern replacement parts like the aluminum master cylinders replacing cast and calling them the same number. The original MarkVII for this part number were cast cylinders which will expand more slowly. I suspect they will afford just a few (precious) more degrees of fluid heat before it allows the same type of blow past failure. The big box stores likely have a mix of cast and AL for this part number.

    Whatever you get, if safety is your ultimate concern monitor for heat. I'm still in the process of researching how to best do this on my car.

    Why monitor for heat is what can happen if you don't- surprises. Like me, Your first indication could very well be when you jump into the turn lane and try to apply the brakes and they aren't there. Luck and quick thibking is all that saved my car - I was able to get back into the center lane mere feet before I would have wrecked by ramming my T5 into 1st at 45 and popping the clutch and turning very aggressively in behind the car that was previously behind and beside me. I then got back into the gas enough to avoid going into a circle and rode the bumper of the guy in front of me through the intersection on a yellow.

    Thats the type of luck required to navigate a foxbody in city traffic and on bad roads for all the years I've been able to. Thank heavens he didn't panic and hit his brakes! I had a partially torn apart interior at the time so my seat belts were out of comission. 45-50 into a stopped car with no seatbelt would have turned out ugly for both me and my car I am certain.

    It makes me continue to evaluate crash cages and 5 point harnesses to see if there is something out there I could tolerate on long road trips. I don't want to give up the driver aspects of my car but I also see the need to increase safety if I'm going to drive a car with the amount of acceleration, handling, and braking performance it now has on tap. I used to hold back and expect stopping drama and I hadn't been because what I built is no longer just a one trick (0-60) pony.

  15. #15

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    Because you gutted your proportioning valve for the 5 bolt and rear disc upgrade you no longer have use of the switch on top of the proportioning valve. The part that would trip the light in the event of a line rupture no longer functions. The low fluid sensor in the new style master cylinder is meant to replace the old proportioning switch. The reservoir on the SN95 is not split like the older 86 master, when the fluid is low because of a rupture the fluid level inside the plastic reservoir is lowered and the light comes on to warn you of a brake issue. To facilitate a warning light on my conversion I used a pigtail from Ford, part number 3U2Z-14S411-NUB to plug into the low fluid sensor on my SN95 master cylinder, this pigtail has three wires instead of the two used on the original switch, find the two wires out of the three that would complete the circuit when the float inside the reservoir is at it's lowest point, cut and connect those two wires to the two wires that were attached to the old proportioning valve switch. You will now have a working light on your dash in the event you lose fluid. You can test it by pushing the float down and it will trip the red light that is also your e/brake light.

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    Quote Originally Posted by mb757 View Post
    Because you gutted your proportioning valve for the 5 bolt and rear disc upgrade you no longer have use of the switch on top of the proportioning valve. The part that would trip the light in the event of a line rupture no longer functions. The low fluid sensor in the new style master cylinder is meant to replace the old proportioning switch. The reservoir on the SN95 is not split like the older 86 master, when the fluid is low because of a rupture the fluid level inside the plastic reservoir is lowered and the light comes on to warn you of a brake issue. To facilitate a warning light on my conversion I used a pigtail from Ford, part number 3U2Z-14S411-NUB to plug into the low fluid sensor on my SN95 master cylinder, this pigtail has three wires instead of the two used on the original switch, find the two wires out of the three that would complete the circuit when the float inside the reservoir is at it's lowest point, cut and connect those two wires to the two wires that were attached to the old proportioning valve switch. You will now have a working light on your dash in the event you lose fluid. You can test it by pushing the float down and it will trip the red light that is also your e/brake light.
    TOUCHDOWN!!!!! as one of our other fellow stanger would say.... This is the answer I've been waiting for confirmation on. I thought this would be the working scenario for the conversion, but no one could or would confirm it. Thank you @mb757 you win the PRIZE!

    Now just to add an additional question to you. I pulled a couple reservoir switches from the boneyard. I believe 2 of the samples in my photo is the p/n that you listed.... If not exact, I'm sure they will do the same job as they are from the non-hydroboost cars.


    I am still curious as to how these plastic bowl reservoirs transfer their low fluid signal down to the senor switch? There seems to be no physical connection between the bowl and the contact point to complete the circuit.... Maybe it's magnetic???

    Name:  20170302_195637.jpg
Views: 372
Size:  89.1 KB

    This is my new Reservoir sold as being for the 1993 Cobra Master Cylinder. It looks just like the later model Fox cars.

    Name:  20170302_193123.jpg
Views: 369
Size:  35.5 KB


    I'LL REPORT BACK WHEN IT'S ALL HOOKED UP AND DONE!

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    Quote Originally Posted by erratic50 View Post
    I suggest a different route for the pump side of your brakes.

    A Lincoln Mark VII master cyl is a 1" bore rather than a 15/16" like is found in the 93 along with the SN95 or the 1 1/8 found in the SVO.

    Many people running the SVO master cyl without the large 73mm diameter single piston calipers report over assisted brakes with poor - very little - pedal travel before lockup. Too little brake rod movement.

    Many I've spoken to that use the 15/16 bore master cyl with stock foxbody booster talk about an under assisted feel with too much pedal travel before lockup and too much pedal pressure required for max braking and even perhaps normal driving situations. Too much brake rod movement for the fox booster.

    I am using the MarkVII master cyl with a simple line adapter available off the shelf at AutoZone. I gutted and plugged the front/rear bias portion of my stock proportioning valve and installed a Summit manual valve at the line Union on the passenger side. Master cylinder you want is part# m1858. Found at advance auto or AutoZone.

    My brakes work very well.

    A great friend of mine also has an 86 mustang and he runs SN95 rear brakes adapted to foxbody rear diff. I run an entire SN95 rearend. I run 99GT brake calipers with Baer rotors in front. He runs 2004 Cobra rotors and calipers up front. This setup functions flawlessly with both configurations and does not mess with the fluid lost warning indicator.

    Now I'm going to introduce somethibg new to worry about.

    I will say from experience that this light won't shield you from overloading brakes and ultimately boiling the brake fluid and losing braking. I did this once recently when one of my 99 calipers did what they are notorious for - stuck at part engagement - which build massive amounts of heat VERY quickly without noticeable input into the steering. I've since replaced the caliper and all is well again but my point is if you want the level of safety in your braking system that this thread seems to lay out as being desired then you need something to sense the temperature of your brake fluid. The warning light won't tell you when the DOT4 is blowing out from the sides of the seal on the master cyl due to heat expansion and is going to push past the seals in your master cyl due to extreme master cyl metal expansion at high heat. There is still enough fluid there that the light won't come on.

    I guess we could call it a down side of the more modern replacement parts like the aluminum master cylinders replacing cast and calling them the same number. The original MarkVII for this part number were cast cylinders which will expand more slowly. I suspect they will afford just a few (precious) more degrees of fluid heat before it allows the same type of blow past failure. The big box stores likely have a mix of cast and AL for this part number.

    Whatever you get, if safety is your ultimate concern monitor for heat. I'm still in the process of researching how to best do this on my car.

    Why monitor for heat is what can happen if you don't- surprises. Like me, Your first indication could very well be when you jump into the turn lane and try to apply the brakes and they aren't there. Luck and quick thibking is all that saved my car - I was able to get back into the center lane mere feet before I would have wrecked by ramming my T5 into 1st at 45 and popping the clutch and turning very aggressively in behind the car that was previously behind and beside me. I then got back into the gas enough to avoid going into a circle and rode the bumper of the guy in front of me through the intersection on a yellow.

    Thats the type of luck required to navigate a foxbody in city traffic and on bad roads for all the years I've been able to. Thank heavens he didn't panic and hit his brakes! I had a partially torn apart interior at the time so my seat belts were out of comission. 45-50 into a stopped car with no seatbelt would have turned out ugly for both me and my car I am certain.

    It makes me continue to evaluate crash cages and 5 point harnesses to see if there is something out there I could tolerate on long road trips. I don't want to give up the driver aspects of my car but I also see the need to increase safety if I'm going to drive a car with the amount of acceleration, handling, and braking performance it now has on tap. I used to hold back and expect stopping drama and I hadn't been because what I built is no longer just a one trick (0-60) pony.
    @erratic50 sound like you had a bit of a white-knuckle driving experience with those brakes!!! Thanks for the great advice.

    I think we can clarify one thing on the master cylinders you spoke of above: The 1993 Cobra M/C is a 1" Bore. However, the 94-95 Cobra M/C is 15/16th.

    All that I have researched states the 93 Cobra M/C coupled to the 93 Cobra B Booster feeding 99 PBR calipers up front and SN95 calipers out back renders a stable breaking system much in mathematical balance as the 1996 v6 cars. If this set-up falls short, I will certainly revisit your set-up. Thanks.

    What you mention about the cast differences of the Lincoln MarkVII and the plastic bowls and their respective properties is an interesting perspective. I guess Ford and the many other manufacturer using plastic bowls simple weighed out the sacrifices and found it to be safe enough to go full production.

    Where it comes to boiling the brake fluids, I believe that to be a real possibility in a seriously spirited driving scenario. However I doubt I'll find myself in that way. I will keep in mind your experience with the 99+ PBR calipers though. I was not aware of their tendencies to stick, as you described. That event is not something good to have happen. I will add to this though: I would suggest any one running these and any calipers for that matter to apply the provided "Organic Brake Grease" that comes in the caliper boxes as New. If you have old boneyard pieces, then buy the grease and lube the guide pins and the pistons. I believe this will stave-off any caliper lock-up. I'm no brake expert though so I'd suggest taking it all serious when brakes are the subject and read-read-read, then follow instructions well...

    Another thing that I plan to write about soon is the used of various brake fluid types. You mentioned one: Dot 4. ....Never mix Dot 3 -4 with Dot 5 and 5.1!!! And Dot 3 has a better life span inside your lines if you happen to NOT change you brake fluid that often. In addition it's boiling point IS lower, if you're road-racing this is a concern .....

    Thanks a bunch @erratic50 for all of you info. Chat with you soon on here somewhere for sure....

    Dwayne

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    Quote Originally Posted by mb757 View Post
    Because you gutted your proportioning valve for the 5 bolt and rear disc upgrade you no longer have use of the switch on top of the proportioning valve. The part that would trip the light in the event of a line rupture no longer functions. The low fluid sensor in the new style master cylinder is meant to replace the old proportioning switch. The reservoir on the SN95 is not split like the older 86 master, when the fluid is low because of a rupture the fluid level inside the plastic reservoir is lowered and the light comes on to warn you of a brake issue. To facilitate a warning light on my conversion I used a pigtail from Ford, part number 3U2Z-14S411-NUB to plug into the low fluid sensor on my SN95 master cylinder, this pigtail has three wires instead of the two used on the original switch, find the two wires out of the three that would complete the circuit when the float inside the reservoir is at it's lowest point, cut and connect those two wires to the two wires that were attached to the old proportioning valve switch. You will now have a working light on your dash in the event you lose fluid. You can test it by pushing the float down and it will trip the red light that is also your e/brake light.
    Ok, @mb757 sorry, I may have to question your premise a bit. No offense, just minds coming together....I went out to the garage to look at my Proportioning/Combo Valve and I noticed that it looks like ding the gutting only effect the rear proportioning of those calipers. So in my understanding, the PV should still be able to register line pressure from the front of the PV/Combo Valve...Talk-me-down

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    FEP Super Member erratic50's Avatar
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    As far as I can tell from the cutaways the low fluid portion is still functional after getting the rear proportioning part of the stock setup.

    Please feel free to disagree and back it up with facts to help us understand why this is incorrect. I'm running the setup I described and I'm reasonably certain the light is still functional or I wouldn't have done this mod for what it's worth. I'm all ears on responses and plan to listen carefully with a deep study of the opinions expressed if they differ - that's for sure.

    100% agree on the grease. My caliper was just somehow bad. It barely had any miles on it at all when it did its minor hang up trick and believe it or not it didn't take any more than aggressive city driving in traffic to experience brake fluid boiling with full synthetic dot4.

    All seems well at the moment in the braking department on my car. The upgraded brakes once again saved my behind as I was in a hurry on the way to the airport. No way the stock brakes would have gotten me stopped and I know I would have been going just as fast with or without the upgraded setup.

    Im not entirely sure what my 100-0 distance actually is but I know I certainly WAY better than stock and tested in as much as of the 80-0 plenty on the way to fly out.

    One time I was revved out in 2nd at around 85 and just ready to bang 3rd when I had to shut it down in a very serious hurry. Very glad the upgrades do their job!

  20. #20

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    Quote Originally Posted by 1200 View Post
    Ok, @mb757 sorry, I may have to question your premise a bit. No offense, just minds coming together....I went out to the garage to look at my Proportioning/Combo Valve and I noticed that it looks like ding the gutting only effect the rear proportioning of those calipers. So in my understanding, the PV should still be able to register line pressure from the front of the PV/Combo Valve...Talk-me-down
    If you gutted your proportioning valve as I did, you removed the piston and spring in the center of the proportioning valve, when you removed the piston you took away the perch that the switch attaches to. There is nothing physically left inside the proportioning valve to trigger the switch to alert you to the differential of pressure in the brake system. When you removed that piston you also removed the ability of the valve to do it's job of distributing the fluid at different levels, that's why you need to install a manual adjusting valve in the rear brake line.

    The photo you had of the reservoir is the same as what I used, the top 2 pigtails that you have in the photo are the style that I used. I believe that the switch is triggered with a magnet in the float. If you look at the plastic reservoir you will see it has one inlet with two chambers inside, the fluid level will lower if a brake line leaks, but it has a divider inside that will hold enough brake fluid over either the front or rear portion of the master cylinder that you will still have functioning brakes and it will alert you to an issue by triggering the light in your dash.
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    The new switch uses a float to trigger the light.
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

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    FEP Super Member erratic50's Avatar
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    Hmmms- mine does not look like the one that's pictured above.

    I suggested Lincoln MarkVII because others have reported line fitment problems going SAE to metric. It's all SAE on the setup I'm running.

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    FEP Senior Member BMW Rider's Avatar
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    The float switch in the reservoir is a magnetic switch. It is simple a low fluid level warning to tell you the reservoir is low. It is a simple courtesy feature to alert you to a minor maintenance item. The brakes may still function perfectly normally.

    The switch on the proportioning valve is a brake failure warning. Its job is to let you know when there is a dangerous condition that will severely limit your braking capability. These are not different ways of doing the same thing, they have very different purposes. It is entirely possible to have a full fluid reservoir and still have a brake failure condition that would cause the warning light to activate due to pressure differential in the two sides of the system.

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    The photo isn't actually from a 86 Mustang, it's a Ford Prop Valve, but not out of an 86. I just used this as an example of what's inside, when I gutted the valve I used a plug in the end of the valve and pulled the little piston in the center of the prop valve out. When you removed the piston the part that the switch sits against to trigger the switch in the event of brake fluid loss is no longer there to make contact with the switch. That's why you should go to the newer master cylinder. I used a SN95 master out of a cobra, which is a metric fitting on a 3/16" line, I made a couple of new lines for my application. If you don't want to or don't have the ability to make a line you can purchase adapters to convert from metric to SAE, Maximum Motorsport also makes pre-made lines, I also moved the manual prop valve next to the master cylinder as it made for a neat and better looking installation rather than put it in the line by the hood hinge. My system works and in the event of a loss of front or rear brakes it will notify me of a loss of fluid. Using the older systems that use a prop valve switch won't give you that option.

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    FEP Senior Member BMW Rider's Avatar
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    Your system won't however warn you if there is an air bubble in the system or if there is an internal bypass failure of the master cylinder or if there is a soft line that has not ruptured but swells under pressure. Of course you should be able to tell when you apply the brakes that something is amiss even with out the light. Be aware that your system would fail some safety inspections if the inspector was thorough and discovered it as it is not operating as intended and required under the regulations the car was originally built to.

    Just to be clear, I'm not criticizing, just informing. I have absolutely no brake warning lights in my car.

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